What the Anesthesiologist Should Know before the Operative Procedure

Airway obstruction in the pediatric population presents unique challenges to the anesthesiologist. It is imperative that the anesthesiologist has a thorough and complete understanding of the following prior to the procedure.

The embryogenesis of the airway

The anatomy of the pediatric airway

The challenge posed by the physiology of the child

The pharmacological differences in the different pediatric age groups

The pathology involved

The psychosocial aspects of providing anesthesia to this age group

The surgery or procedure to be undertaken

A comprehensive knowledge of the anesthetic equipment

And, finally, the different anesthetic options available

Embryogenesis of the airway

The embryonic phase: This phase includes the initial formation of the bud to the differentiation of the bronchi to segmental bronchioles.

The fetal phase: is further subdivided into

The pseudoglandular phase: where the lung tissue appears like glands.

The canalicular phase: corresponding to the development of terminal bronchioles up to the origins of the formative acinii. Early stages of gas exchange are possible, and the end of this stage is associated with the production of surfactant.

The saccular phase: where alveoli are formed. Gas exchange mechanisms are better developed as are the cells that produce surfactant.

The postnatal phase: consists of expansion and maturation of the lung tissue.

The above understanding is important, particularly since children are being delivered and considered viable at very young ages. Therefore, a child delivered in the 24th week of gestation will still be in the canalicular phase of development, making management of these children very difficult.

Anatomical differences of the pediatric airway

A child is not a small adult and nowhere is this more significant than in the management of the airway. The following are some of the differences between the pediatric and the adult airway (Table 1).

Table 1.

Characteristic

Pediatric

Adult

Head and occiput

Large compared to the body

Reaches adult proportions by school age

Tongue

Large compared to the oral cavity

Epiglottis

Large and floppy and omega shaped

Stiffer and smaller and U shaped

Larynx

Located at approximately C4

Located at C6

Angle of the cords

Cords are angulated anteriorly and deep seated

Cords are horizontal

Narrowest point

Cricoid

Glottis

Arytenoids

Large and prominent

Not so prominent

Physiological differences

The trachea is developed as a bud from the primitive foregut. The laryngotracheal groove separates the airway from the esophagus. The tracheobronchial tree develops from the endoderm, while the lung tissue develops from the mesoderm. The lungs have three distinct phases of development.

The physiology of the child differs significantly from that of the adult in almost every characteristic. Understanding them is essential in providing a safe anesthetic for the child. The immaturity of the respiratory, cardiac, hematological, renal, endocrine, liver, skin, and the neurological systems further complicates matters.

Pharmacology

The pharmacokinetics and the pharmacodynamics differ significantly in the child. The large volume of distribution, the immaturity of the liver and kidneys, and the differences in the composition of plasma proteins contribute to these.

The pathology of the lesion

Understanding the pathology of the lesion is crucial to the management of the obstructive lesion in the pediatric airway. The lesions can be broadly classified as congenital and acquired. The congenital lesions may be associated with a syndrome or may be isolated lesions. The acquired obstructive lesion may range from acute infective lesions to foreign body aspiration to trauma. Each of the above presents its own unique challenge.

Psychosocial aspects to the management of a child coming in for a procedure

Understanding the psyche of the child is of paramount importance while dealing with acute airway obstruction. For instance, a child with acute epiglottitis has to be treated with utmost caution. If the child were to become agitated, the small reserves holding the child may become inadequate, leading to disastrous consequences. Though the main responsibility of the pediatric anesthesiologist is to treat the child, it is necessary to recognize that the parents and the child are one unit, and the anxiety of the parent rubs off on the child just as the reassuring effect does.

The surgery or procedure

A comprehensive understanding of the procedure/surgery along with the sequence in which it is to be done helps with tailoring the anesthetic to the procedure. For example, if a flexible fiberoptic nasolaryngoscopy is to be done to assess the movement of the cords and to assess laryngomalacia, it is necessary for the child to be breathing spontaneously and fairly lightly. While a rigid tracheoscopy/bronchoscopy is being done, it is necessary for the child to be under a fairly deep level of anesthetic to prevent trauma to the trachea/bronchus by the rigid scope.

The equipment

When dealing with a child with an airway obstruction, it is incumbent on the anesthesiologist to have a plan A, a plan B, a plan C, up to a plan Z. Being able to adapt to the situation means being ready for the situation, which means anticipating the situation. Communication with the endoscopist/surgeon is essential. A range of airway equipment from different blades, handles, airways, tubes, cricothyroidotomy sets, equipment for jet ventilation and for a tracheostomy should all be tested and readily available.

The anesthetic needs

A decision needs to be made regarding the type of anesthetic required. Spontaneous ventilation versus controlled ventilation, inhaled agents versus intravenous anesthetics, narcotics versus NSAIDs versus topicalization are some of the decisions that need to be made

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Assessing the urgency of the situation is part of the clinical decision making in a child with a pediatric airway emergency. Assessment should include:

Emergent conditions

In the event of impending failure, little time should be lost in obtaining further tests or investigations, especially, if a procedure could be therapeutic. Though certain types of lesions are likely to cause extenuating circumstances, it is more a question of the child's immediate state of health which dictates whether the situation is emergent or not. For instance, epiglottitis is a disease which has history of rapid progression that a definitive airway should be obtained in a controlled setting as soon as possible. Foreign bodies could also lead to airway compromise, which could change by the minute.

The following are some acute, life-threatening events (ALTE) related to upper airway obstruction:

Airway foreign body

Angioneurotic edema

Epiglottitis

Trauma/burns

Retropharyngeal abscesses

Urgent conditions

Poiseuille's law states that flow is directly proportional to the 4th power of the radius of the tube.

Algorithm 1

V =δPπr48ή1

where V is the flow, δP is the difference in pressure at the two ends of the tubular structure, r is the radius of the tube, and ή is the viscosity.

A tracheal size of 4 mm has a radius of 2 mm. One millimeter of edema in this trachea effectively changes the radius to 1 mm. As the flow is directly proportional to the 4th power of the radius, halving the radius, as in this case, decreases the flow by a factor of 16 (2 to the power of 4). However, Poiseuille's law holds true for laminar flow and does not account for turbulent flow. In a child with an obstructive pathology of the airway, the flow is likely to be turbulent. In this situation, Fanning's equation expresses the flow characteristics.

Algorithm 2

V2 = ΔPπ2r5 1µf

Where µ is the density and f is the Fanning's friction factor. As is clear halving the radius here would result in a decrease in square of the flow by a factor of 32.

The essence of the above argument is that a child with moderate airway obstruction could rapidly deteriorate to one with severe airway obstruction due to the flow characteristics. All children with moderate obstructive features should be treated expediently for this reason.

Mild airway obstruction

In children with mild airway obstruction there is often time to obtain further investigations in the form of laboratory studies and radiological studies. Laboratory studies including a complete blood count and arterial or venous blood gases may be helpful, but one should not insist on these at the expense of aggravating the child. Clinical assessment will probably supersede any laboratory or radiological assessment. A plain x-ray may be useful in locating a foreign body, and more sophisticated studies such as a computerized tomography or a magnetic resonance imaging study may be helpful in children with peritonsillary and retropharyngeal abscesses.

2. Preoperative evaluation

History and physical examination

A history and physical examination should be done expediently but thoroughly. History should focus on the respiratory system

Onset of symptoms

Presence of stridor. Nature of the stridor: inspiratory (surpaglottic), expiratory (tracheal) or biphasic (glottic or subglottic)

Presence of an upper respiratory infection

Cough. The nature of the cough can be quite illuminating, for instance, a cough which is of a sudden onset is likely to be due to a foreign body aspiration, a painful cough is likely to be due to laryngitis, in which case it is harsh and has a barking quality to it, or tracheitis, which is associated with chest pain on coughing. Pharyngitis is associated with a post nasal drip and a pneumonia begins as a dry cough progressing to a productive cough.

Bronchopulmonary dysplasia

h/o foreign body ingestion or aspiration

Croup

Snoring and sleep apnea

Asthma

Dyspnea

Cardiovascular system: History of congenital cardiac defects, cyanosis, pulmonary hypertension, presence of persistent fetal circulation, symptoms of heart failure such as diaphoresis, breathlessness on feeding, and pedal edema should be obtained.

Gastrointestinal: History of reflux disease, its severity and medications related to it, history of foreign body ingestion, dysphagia, drooling, nausea, vomiting, and abdominal surgeries should also be obtained.

Genitourinary: Pregnancy, menses, urinary symptoms, urinary tract infections, and renal failure are some of the issues that need to be inquired about.

Hematological system: Anemia, bleeding disorders, and transfusion history are important.

Other history specific to pediatrics:

Birth history

Prematurity

Immunization history

Nutrition and eating habits

Developmental history

Environmental, including exposure to smoking

Rash

Syndromes

Sleep patterns

Dentition (loose teeth/braces)

For the older child, drug and tobacco use should be inquired with sensitivity as should a sexual history.

Syndromes and disease associations

Family history: Any adverse reaction to anesthesia (malignant hyperthermia)?

Medication: A physician should be aware of the medications that a child is taking. Children with attention deficit disorder may be on drugs that have a direct effect on the anesthetic. Medications for hyperactive airway disease and their compliance may be very important in a child with airway obstruction.

Physical examination

The most important question that needs to be answered is whether the child is in or at risk of respiratory failure. Clinical signs of respiratory distress are usually fairly clear-cut, though in some instances they can be subtle. Physical examination should follow the usual dictum of inspection, palpation and auscultation.

Inspection: Some of the signs of respiratory distress are obvious on inspection and include:

Tachypnea

Cyanosis

Increasing oxygen requirement

Head bobbing

Nasal flaring

Choking or drooling

Gasping for air

Facial and tongue swelling

Use of accessory muscles of respiration

Chest and suprasternal retractions

Diaphoresis

Adoption of certain postures such as a sniffing position or a tripod position

Obtunded sensorium or panic

Auscultation: can often be quite useful. Wheezing localized to one side suggests a foreign body. A silent chest is probably of more significance than otherwise. Bradycardia and tachycardia are often indicators of an acute respiratory problem. Murmurs are common in pediatrics, some of them benign and others not so. Sinus arrhythmia and pulsus paradoxicus are often exaggerated in children. Examination should be done in a manner that does not cause agitation in the child as this could precipitate further deterioration in the respiratory distress.

Laboratory tests

Noninvasive measurement of pulsus paradoxicus, transcutaneous measurement of carbon dioxide, and arterial blood gas analysis are some of the physiological and laboratory tests that may give a clue to the severity of upper airway obstruction. A complete blood count may be useful to assess the oxygen-carrying capacity. Pulmonary function tests can provide crucial information regarding the type and degree of obstruction in the more chronic setting. However, it ought to be stressed that these investigations should not delay the treatment of an acute airway obstruction in a child.

In children with heart disease, an electrocardiogram may be useful, whereas in others who are a bit older, a stress test may be helpful. A cardiac catheterization or the results of a recent one can give information as to the anatomical, physiological, pathological and functional nature of the disease.

Radiological examination: Plain x-ray of the chest, AP and lateral pictures of the airway, fluoroscopy, computerized tomography and magnetic resonance imaging may all have a role in the investigation of upper airway obstruction. Information from these may be extremely useful to the anesthesiologist, particularly regarding possible airway foreign bodies, airway compression, and lung pathology. However, one should never delay the procedure to obtain these in the presence of severe airway obstruction.

Flexible fiberoptic nasolaryngoscopy: A flexible fiberoptic examination of the upper airway is often done in an outpatient setting. The findings of this examination can be useful to the anesthesiologist.

3. What are the implications of co-existing disease on perioperative care?

Congenital syndromes

Several congenital syndromes are associated with airway abnormalities which could compound the difficulty in the management of airway obstruction in these children. Moreover, these syndromes by inference, have other associated systems involved, including but not limited to the cardiovascular system, skeletal system, gastrointestinal system, renal and hematological systems. Some fo the common syndromes and the airway problems are listed in the following tabular column.

The above list is by no means complete nor does it include all the described abnormalities of the named syndrome, but it highlights the difficulties when treating children with these syndromes.

Prematurity

Prematurity affects almost every organ system and hence has a huge impact on anesthesia. A child born before 37 weeks of gestational age is considered premature, just as a child who is born at 24 weeks. Obviously these children have an enormous difference in their development, morbidity and mortality figures when children with mild prematurity are compared with premature children born at 24 weeks. The following are but some of the challenges one faces when providing anesthesia to the premature infant.

Altered thermoregulation

Respiratory immaturity

Apnea of prematurity

Bronchopulmonary dysplasia

Respiratory distress syndrome

Cardiovascular immaturity

Persistent fetal circulation, patent ductus arteriosus

Non compliant ventricles

Retinopathy of prematurity

Anemia/polycythemia and fetal type of hemoglobin

Renal immaturity

Hypoglycemia and problems with glucose metabolism

Hyperbilirubinemia

Immunological immaturity

Neurological-intraventricular hemorrhages, neurological immaturity

Gastrointestinal - Necrotizing enteroclitis. Reflux disease.

Cardiovascular system

Murmurs

Congenital heart disease

Endocarditis prophylaxis

Heart failure

Murmurs of the heart are common in childhood, and an audible murmur may be found in as many as a quarter of all children. While an asymptomatic murmur is likely to be benign, not all of them are. The discriminative value of clinical examination to differentiate benign murmurs from those with associated cardiac defects is quite high; however, the studies that have demonstrated these findings involved pediatric cardiologists. Therefore, when possible, clinical examination should be corroborated with an echocardiogram when a new murmur is identified.

Congenital Cardiac Diseases: Airway abnormalities are frequently associated with congenital heart disease (CHD). When confronted with a syndrome which has known associations with heart disease, a thorough evaluation should be done when possible. CHD can be complex and the understanding of the anatomy, the physiology, the pathology and the surgical correction often requires specialist knowledge. Pediatric anesthesiologists are well trained to assess and treat these children with CHD. Even so, extra care needs to be exercised when dealing with children with CHD. Discussing with the pediatric cardiologist regarding the level of optimization of the disease as well as understanding the reasons behind the treatment can be useful in the management of these children. Ventilatory strategies, hemodynamic goals, airway management plan, invasive monitoring, postoperative care and acceptable parameters need to be defined before anesthetizing these children.

Infective endocarditis (IE) prophylaxis: The American Heart Association revised the IE prophylaxis guidelines in 2007. A summary of the guidelines is provided in Table 5.

Table 5.

Candidates for antibiotic prophylaxis for endocarditis (2007 AHA Guidelines)Patients with prosthetic valvesHistory of previous endocarditisCongenital cyanotic lesions that are unrepairedCongenital lesions repaired with a prosthetic device or material up to 6 months following the procedureRepaired defects with residual shuntsHeart transplant recipients with a valvulopathy

Heart failure: Signs of heart failure are often subtle in children and should be sought out specifically. Diaphoresis, poor feeding, failure to thrive, edema and hypotension are some of the symptoms and signs of heart failure in children. Small children are often unable to explain their symptoms, and it is often necessary to obtain these vicariously. Heart failure in children can masquerade as respiratory infections, asthma, or even colic.

Respiratory: Underlying conditions of the respiratory tract can confound the acute problem. Reactive airways disease of childhood is fairly common. A full history as to the extent of the disease, medications being used, last dose, need for hospitalization, need for emergency room visits, history of prematurity/bronchopulmonary dysplasia, recent upper respiratory tract infections and lower respiratory tract infections are some of the details that need to be ascertained.

Upper respiratory infection and general anesthesia

URI are very common in children. Epidemiological data reveals that children could have up to eight URI's in a year. Data also suggests that the risk of general anesthesia in children with an active or recent URI is significantly increased. These children are at a higher risk for perioperative complications such as hypoxia, atelectasis, laryngospasm, bronchospasm and pneumonias. The most cautious recommendation is wait six weeks after a URI before administering a general anesthetic to mitigate the risks.

The dilemma is to know when to proceed and when to postpone the procedure There are some factors which appear to increase the risk of these complications. The younger the child the greater the risks of the complications. Associated lower respiratory signs such as a productive cough, a croupy cough, lung signs in the form of wheezing, a high fever (>101 F), constitutional symptoms such as decreased appetite and activity and the need for endotracheal intubation increase these risks significantly. The recommendation in this situation is as follows:

Proceed if the surgery is urgent. If not, look for the above signs, in the presence of any of the above signs, delay surgery. In the case of a simple URI without lower respiratory signs or symptoms, delay surgery by at least two weeks. If associated with lower respiratory signs, delay surgery for at least 4-6 weeks.

In the absence of the said signs, one can proceed with surgery as long as endotracheal intubation is not essential. If intubation is required, consider postponing the procedure. If the procedure can be done without intubation, then one can proceed with the anesthetic for the procedure.

Renal-GI: Premature infants have a poorly developed renal system. Their ability to handle salt loads is significantly decreased. Their glomerular filtration rate is a fraction of the adult values. The kidneys of a newborn are still immature and have not developed fully. Glomerular filtration rate, which is used as a measure of renal function, is as low as 21 mL/min/1.73 m2 in the newborn. It increases to 60 mL/min/1.73 m2 by the age of 2 weeks. It reaches adult values of 90 mL/min1.73 m2 by about 2 years. This should be factored in when designing a fluid management plan for the neonate.

Neurologic: The brain is still developing in the newborn child, and myelinization and neuronal development takes several years. Several neurological problems could interfere with the anesthetic management of the child. Hydrocephalus with or without a raised intracranial pressure could be present. Seizure disorders are common in children and can be a source of concern, as can the anti-epileptic drugs (AED) or treatment regimes such as ketotic diets. Attention-deficit/hyperactivity disorder and autism are also frequently encountered in this population. Developmental delay and neurological immaturity can be a cause of central apnea.

Endocrine: The immaturity of the liver in the newborn can predispose them to hypoglycemia in the perioperative period. Juvenile diabetics are often very brittle, and their management can be demanding. Children with Beckwith Weidemann Syndrome are prone to develop hypoglycemia. Children with DiGeorge Syndrome are prone to develop hypocalcemia as a result of hypoparathyroidism.

Hematological: It is customary to divide them into children less than 4 months old and those more than 4 months old. The reasons for this are as follows. In the first 4 months of life there is a decreased production of erythropoietin and smaller total blood volumes (even though they have a larger volume for weight). There is a transition from the fetal type of hemoglobin to the adult variety over this period. The reason for a decrease in erythropoietin levels is a consequence of normal oxygen levels in the newborn period when compared to the relatively hypoxic intrauterine milieu. The fetal hemoglobin has a higher affinity for oxygen and hence the oxygen dissociation curve is shifted to the left. The implications of this are important in so far as an acceptable hemoglobin level in an adult may not equate to an acceptable level in these children. P50 is the PO2 at 50% SO2. The P50 of adult hemoglobin at 37 degrees and a pH of 7.4 is 27 mm Hg. The P50 of fetal hemoglobin at 37 degrees and a pH of 7.4 is 19 mm Hg. The P50 of an infant beyond 3 months of age rises to about 30 mm Hg. A hemoglobin level of 7 g/dL will be able to carry the same amount of oxygen whether it is fetal Hb (HbF) or adult Hb (HbA); the unloading characteristics of the fetal hemoglobin could, however, mean that this level of hemoglobin is inadequate for the neonate. To give an example, a hemoglobin level of 10g/dl in an adult with a P50 of 27 mm Hg equates to just 6.8 g/dL in a 2-month-old child with a P50 of 24 mm Hg. Using the above calculations, a neonate less than 2 months of age will require a hemoglobin level of at least 12 g/dL, which is considered to be the equivalent of 8 g/dL in an adult.

b. Cardiovascular system

N/A

c. Pulmonary

N/A

d. Renal-GI:

N/A

e. Neurologic:

N/A

f. Endocrine:

N/A

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

N/A

4. What are the patient's medications and how should they be managed in the perioperative period?

Children, like adults, can have a wide variety of associated diseases for which they may be on different medications. A thorough history will help identify problems with drug interactions with anesthetic agents. Of particular concern are drugs taken for gastroesophageal reflux disease (GERD) and reactive airway disease. They may also be on corticosteroids for a wide variety of reasons. The role of stress doses of steroids is not well established, but steroids in this group may well be indicated in the presence of hemodynamic instability unresponsive to conventional methods of treatment.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

N/A

i. What should be recommended with regard to continuation of medications taken chronically?

Chronic medications, unless likely to interfere with the anesthetic, should be continued in the perioperative period if possible. It is often difficult to achieve therapeutic steady state levels in children, and interruption in the medication regimem is poorly tolerated.

j. How To modify care for patients with known allergies -

Children with myelodysplasias and urinary tract abnormalities are at high risk for latex sensitization and for latex allergy. Latex precautions in these children decrease the risk of latex sensitization. Latex has been identified as the second most common cause of anaphylaxis in the perioperative period in the last two decades. The allergy to natural rubber latex (cis-1,4-polyisoprene), which is commonly obtained from the Hevea brasiliensis tree, is due to the proteins in it. The proteins are denatured and hydrolyzed in the process of making the product. There are several proteins that have been identified as the cause for the allergy. Of these, Profilin and Hevein are the two most common proteins responsible for the allergy.

Allergy to latex may range from simple irritant dermatitis and contact dermatitis to anaphylaxis. Identification of at risk children is the cornerstone in preventing latex related allergies in the perioperative period. Presentation in the operating room may be insidious or acute and can be difficult to diagnose. Rash, hypotension, bronchospasm, vasodilation, increased vascular permeability, and cardiovascular collapse can all occur. A high degree of suspicion in the at-risk group is key to the diagnosis.

Diagnosis in the operating suite is usually clinical. Later on, in vitro testing, blood tests such as β-tryptase levels, serum specific IgE antibodies to latex and skin testing (not approved in the US) can all point to the diagnosis.

Prevention is by far the best treatment in these children. A latex-free environment eliminates this risk. The Food and Drug Administration has mandated that all equipment used in the perioperative period containing latex be labeled as such. In the event of anaphylaxis in the operating room, latex as a source of the anaphylaxis should be entertained in the differential diagnosis. Treatment should include removal of the offending article, supportive treatment in the form of intubation, oxygen, bronchodilators, antihistamines such as diphenhydramine, epinephrine and other vasoactive agents, corticosteroids, H2 receptor blockade, and intravenous fluids can all be helpful.

l. Does the patient have any antibiotic allergies- [Tier 2- Common antibiotic allergies and alternative antibiotics]

N/A

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

MH is caused by an abnormality in the skeletal muscle which leads to an enhanced activation of the ryanodine receptor 1 (RYR1), which in turn leads to excessive calcium release. In the classic form of the disease, the RYR1 gene mutation is responsible for this anomalous response to a trigger (potent inhaled anesthetics and succinylcholine). Of the other loci proposed as sites responsible for MH, only the dihydropyridine receptor has been linked by studies so far.

Clinical presentation of MH

Respiratory features: Increased metabolic rate leading to increased oxygen demand, respiratory acidosis despite increased minute ventilation, PetCO2 greater than 55 mm Hg with ventilation deemed appropriate for age and weight of the patient are some of the respiratory signs.

Treatment of MH

If MH is suspected, immediately discontinue the potential trigger. Stop the procedure and notify the surgeon. Switching over to another circuit that is free of inhaled agents using high gas flows (100% O2) to wash out the remaining agent should be instituted immediately. Help should be sought locally within the department and also nationally via the available national hotline 1-800-MH-HYPER (644-9737). Laboratory evaluation for MH should be undertaken. Institute therapy with Dantrolene, 2.5 mg/kg, up to a total dose of 10 mg/kg. Continue supportive measures in the form of intravenous fluids, ionotropic support if required, placement of additional invasive monitors, treatment of hyperkalemia, acidosis and active cooling.

Anesthesia for a child who is suspected to be MH susceptible: A thorough history regarding the supposed event and the family history should be obtained. If indeed a child is considered susceptible for MH, a nontriggering anesthetic should be used, avoiding potent inhaled anesthetics and succinylcholine.

Drugs considered safe for use in a person with suspected MH are as follows: Narcotics, barbiturates, benzodiazepines, nondepolarizing muscle relaxants, local anesthetics, ketamine, propofol, dexmedetomidine, anticholinergics, anticholinesterases, nitrous oxide, and NSAIDs.

5. What laboratory tests should be obtained and has everything been reviewed?

In general, laboratory investigations are not required in healthy children. The need for these tests is dictated by the underlying pathology and co-existing diseases. In premature infants and neonates, a blood glucose level immediately prior to the procedure should be done and repeated as required. Hemoglobin levels are useful in these children for the reasons mentioned under hematological system. Children on parental nutrition and children with renal insufficiency should have had serum electrolytes measured on the day of the procedure. Coagulation studies in general are not required unless the history is suggestive. Children with congenital heart disease should have had an electrocardiogram done recently as well as an echocardiogram. Results of recent cardiac catheterization and cardiac MRI if available should be reviewed. A chest x-ray is useful in these children to assess various problems associated with airway obstruction. In a child with trisomy 21, a flexion extension x-ray can help identify atlantoaxial instability. However, none of these investigations should delay an airway emergency.

Intraoperative management

What are the options for anesthetic management, and how to determine the best technique?

An anesthetic should be tailored to the child and to the procedure.

Requirements should be assessed preoperatively and definite goals set.

Benumof and Donlon in 1996 put forth some objectives that are useful to consider.

Airway: The airway is shared with the surgeon and inadequate control of the airway in a child with airway obstruction conflicts with the principles of anesthesia. It is essential to develop a trust with the proceduralist and to delegate certain responsibilities to the surgeon. In a child undergoing a flexible nasolaryngoscopy it is important for the surgeon to see the dynamic nature of the nasopharynx so as to identify problems such as laryngomalacia and vocal cord paresis, while at the same time one should be prepared for a laryngospasm by having a functional intravenous line for this emergency.

An anesthetic should be tailored to the child and to the procedure. Requirements should be assessed preoperatively and definite goals set. Benumof and Donlon in 1996 put forth some objectives that are useful to consider. Furthermore, it is necessary to have an understanding about the causes of airway obstruction to be able to devise a plan for the anesthetic management. Anesthesia for obstructive airway problems is a catalog of compromises.

Anesthetic techniques available for airway procedures

The following are some of the ventilatory strategies available:

Spontaneous ventilation with topicalization, with or without sedation

Spontaneous ventilation under general anesthesia

Low frequency jet ventilation

High frequency jet ventilation

Periodic ventilation with intermittent apnea

Microlaryngoscopy tube

Ventilation via a bronchoscope

Tracheostomy or cricothyroidotomy

Causes of airway obstruction emergencies

Congenital neck masses:

Cystic hygromas, teratomas, hemangiomas and lymphangiomas are some of the causes of emergent airway obstruction in the newborn. The incidence of significant obstruction is higher if these masses are in the anterior triangle of the neck.

Things to consider

Use of narcotic in children with co-existing obstructive sleep apnea syndrome

Use of nonsteroidal and anti-inflammatory drugs

Intravenous vs inhalational anesthesia for maintenance

Contamination of the operating room suite with inhaled anesthetics using an open technique should also be taken into consideration.

Secretions need to be controlled and can be effectively achieved with the use of anticholinergics.

A depth of anesthesia which allows for an unhindered examination of the airway while at the same time allows spontaneous ventilation is optimal.

Oxygen is often a necessary supplement in these children, this needs to be weighed against the risk of combustion.

Local anesthesia depresses the reflexes and this should be weighed against the risk of aspiration.

Smooth emergence needs to be weighed against safe extubation.

Deep vs awake extubation

Time needs to be weighed against the need to complete the procedure without the added stress

Extension of the neck needs to be weighed against the safety of the spine

Permissive hypercapnia should be weighed against the need for spontaneous ventilation

Achieving an adequate depth of anesthesia to prevent an adrenergic response without causing hypotension is another challenge

Backup strategies

Anesthesia for individual airway obstructive pathology

The following are examples and exceptions in the anesthetic techniques for each group of patients. It isn't a complete list, but the techniques described are common and can well be adapted to any situation. They are my preferred techniques in each situation.

Anesthesia for supraglottic lesions:

Anesthetic management of supraglottic lesions is different from glottic and subglottic lesions in so far as definitive control of the airway is possible. This distinction apart, induction and postanesthetic recovery still pose challenges.

Supraglottic obstructive airway lesions include surgery for rhinological lesions, obstructive sleep apnea syndrome (OSAS), and pharyngeal lesions. Of these, it is worthwhile reviewing OSAS and the anesthetic technique for children with this syndrome.

The incidence of OSAS is highest in children between 2 and 8 years. This is thought to be an indirect result of the hypertrophy of the lymphoid tissue in relation to the size of the airway. Having said that, lymphoid hyperplasia in the form of adenotonsillar hypertrophy correlates poorly with OSAS. It has been postulated that other causes such as allergic rhinitis, poor pharyngeal muscle tone, midface hypoplasia, obesity and genetic factors also play a role in childhood sleep disorders. Nearly all the syndromes that have been listed as being associated with a difficult airway have also been associated with OSAS.

Of the main differences in polysomnography between adults and children, the two that stand out are 1) apnea, which is defined as a cessation of breathing lasting 10 sec or longer in adults, is defined as cessation of breathing lasting two breaths or longer in children; and 2) an apnea hypopnea index of less than 5 is considered normal in adults, whereas an index of less than 1 is considered normal in children. An AHI of greater than 10 is considered as severe OSAS. Similarly, a Respiratory Arousal Index (RAI) of less than 1 is considered normal, whereas an index of greater than 8 signifies severe OSAS. There are several other differences, including the definition of hypopnea and hypopnea desaturation, but they are purely for the purposes of the study itself. Diagnosis is made on the basis of history, examination, nocturnal oximetry and polysomnography.

Treatment of OSAS in children is primarily by adenotonsillectomy. Though two distinct types of OSAS have been identified, both appear to respond to adenotonsillectomy equally well. Type 1 is associated with adenotonsillar hypertrophy, whereas type 2 adenotonsillar hypertrophy is not prominent. Instead OSAS is associated with obesity in these children.

Anesthesia for these children should take into consideration the use of narcotics and postoperative care in a monitored setting. Steroids appear to help with inflammation and pain in these children. Antiemetic prophylaxis in children over the age of two years is certainly useful. The role of nonsteroidals and antiinflammatories is controversial, with some institutions believing that they increase the risk of postoperative bleeding, while others do not subscribe to this view.

Anesthesia for epiglottitis

Epiglottitis is an uncommon but life-threatening condition that we as anesthesiologists come across. It is of bacterial etiology. The most common organism responsible for this disease today is group A β hemolytic streptococci. Until recently, Haemophilus influenzae B was the most common organism responsible for this disease. Another change that has been observed regarding the evolution of this disease is the population at risk. Children between the ages of 3 and 8 were most commonly affected. With effective immunization against HiB, older children and adults are being affected more often. The presentation is acute with respiratory distress, fever, drooling, dysphagia and a muffled voice (hot potato voice). Treatment of this condition should be expedient and under controlled settings. An experienced anesthesiologist and an otorhinolaryngologist need to be present while attempting to control the airway in the operating room. Anesthesia is often induced in the sitting position and every effort is made not to use positive pressure ventilation as the epiglottis may act as a ball valve leading to barotraumas. The ETT often needs to be downsized significantly to avoid trauma. Treatment is then instituted with appropriate antibiotics and steroids. Extubation criteria should be carefully assessed and a decrease in edema documented either with a flex nasolaryngoscopy or by the leak test before extubation.

Anesthesia for glottic lesions

Anesthesia for glottis and pharyngeal lesions pose the greatest challenge to the anesthesiologist. Several techniques are available, highlighting the absence of "the best" way to provide anesthesia and for airway management. Suspension laryngoscopy is often required while working on the glottis. This requires a deep plane of anesthesia to prevent adrenergic response to the laryngoscopy, which has been described as one of the most painful stimuli known to man. The options for airway management include spontaneous ventilation, controlled ventilation with a small ETT with the surgeon working around the ETT, jet ventilation usually supraglottic and intermittent periods of apnea.

The needs of the surgeon, and the pathology itself, define the methodology used in most instances. For example, if the procedure is a long one, intermittent apnea is unlikely to be of help, lesions such as vocal cord papillomas are better managed with spontaneous ventilation, because jet ventilation may help to seed the papilloma into the distal tracheal bronchial tree, a child with congenital heart disease and pulmonary hypertension is unlikely to tolerate the hypercapnia that is associated with shallow breathing of spontaneous ventilation, and an ETT would distort the symmetry of the cords, which needs to be assessed in procedures such as injection of the vocal cords for vocal cord palsy.

Anesthesia for airway papillomas: Anesthesia for airway papillomas is quite distinct in many ways and is worth discussing. The controversy at the fore is whether to use a muscle relaxant or not. While muscle relaxants have been used safely and effectively in the past, arguments have been made against its use. Of concern is the loss of posterior pharyngeal muscle tone, leading to complete airway obstruction. The use of spontaneous ventilation allows the use of FiO2 less than 30%, decreasing the risk of airway fires. Spontaneous ventilation also avoids the need for positive pressure ventilation with its attendant risk of distal seeding of the papillomas. Postoperatively, croup is quite common and nebulized racemic epinephrine and steroids help with this problem. If laser is to be used, the risks include airway fire, thermal injury to tissue, injury to personnel in the OR and infective risk due to vaporized viral agents. All precautions to eliminate these risks should be taken.

Anesthesia for subglottic lesions

Subglottic lesions are approached with an endoscope. A rigid endoscopy has advantages and disadvantages for us as anesthesiologists. It is possible to ventilate the child through a bronchoscope. The disadvantage is that the child needs to be under a deep plane of anesthesia as any movement of the child during this process can be catastrophic. Anesthesia can be provided via the bronchoscope using inhaled anesthetics or with intravenous agents. At times it is also possible to use a small ETT and have the surgeon pass his/her bronchoscope to the side of the ETT. Jet ventilation or mask ventilation with periods of apnea is a possibility, too.

Anesthesia for airway foreign bodies

Spontaneous ventilation is desirable for two reasons. The first is to ensure that the FB is not pushed further distally with the use of positive pressure ventilation and, second, to avoid potential barotrauma from a ball-valve effect of the foreign body. Oxygen can be used as required as long as there is not a source of ignition. A still patient is a requirement when a rigid bronchoscope is in place. Topicalization of the cords and trachea helps reduce the anesthetic requirement.

What are the common intraoperative complications and how can they be avoided or treated?

Anesthesia for obstructive airway lesions is associated with several significant complications unique to the airway. The key to a successful anesthetic is to be cognizant of these complications and to avoid them if possible and, if not, to treat them promptly and appropriately.

Respiratory:

Laryngospasm

Bronchospasm

Airway trauma

Pneumothorax

Postobstructive pulmonary edema (POPE)

Hypoxia / hypercarbia

Atelectasis

Lower respiratory tract infections

Aspiration

Respiratory depressions / apnea

Postintubation or instrumentation croup

Cardiovascular

Hypotension

Bradycardia

Other arrhythmias

Cardiac arrest

Other

Postanesthesia emergence delirium

Postoperative bleeding

Urinary retention

Hypothermia

Pyrexia

Postoperative nausea and vomiting

Hypoglycemia

Medication errors

Malignant hyperthermia

Electrolyte disturbances

Neurological

Nerve injury

Hypoxic brain injury

Death

Several of these potential complications have been discussed in the text above. The essence of avoiding these complications is attention to detail and preparation. Many studies have shown inadequate preparation to be an important reason for anesthesia related complications. Age is a factor and prematurity an even more important one. The level of training and the experience of the anesthesiologist also appear to be determinant factors. Nevertheless, prevention failing, early recognition is perhaps the best strategy in obviating these complications.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

a. Regional anesthesia

N/A

b. General Anesthesia

N/A

c. Monitored Anesthesia Care

N/A

6. What is the author's preferred method of anesthesia technique and why?

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

N/A

c. Postoperative management

Postanesthesia management is just as important as pre- and intraoperative management because children with obstructive airway lesions are at a heightened risk of developing problems in the immediate aftermath.

Questions that need to be answered include:

Duration of postanesthesia care unit observation

Discharge criteria

Should the child be discharged home or should the child be observed overnight?

Several criteria and scores are available regarding discharge; however, the decision should be made in context. A premature child with a postconceptual age of 50 weeks, who has had general anesthesia, certainly warrants observation overnight, whereas a term infant of 45 weeks could potentially be discharged home if safety criteria are met. Similarly, the prudent disposition of a child with severe OSAS and high AHI would be the intensive care unit for observation. The younger the child the lower the threshold for admission or observation; similarly, indications for blood tests and x-rays should be based on the child, procedure and the anesthesia that the child has received. The underlying principle is the safety of the child. A child who has some respiratory insufficiency may very well be managed with noninvasive ventilatory strategies such as CPAP or BPAP. A child with a difficult airway should be extubated under conditions that are optimal for emergency reintubation. Though the temptation is to use oxygen indiscriminately in the postoperative setting, it should be realized that oxygen is a therapeutic intervention and can have serious consequences like retinopathy of prematurity and respiratory distress syndrome. Sometimes the best strategy is masterly inactivity.

(The authors evaluated 203 children for croup and epiglottitis. Differentiating characteristics in the early part of disease were that croup presents with cough and no drooling while epiglottitis presents with drooling and no cough.)